1. Field of the Invention
The present invention relates to an optical pickup transport mechanism suitably for use in CD-ROM drives and the like.
2. Description of the Related Art
A transport mechanism in which a screw shaft is rotated by a stepping motor to linearly reciprocate a head member has been adopted in magnetic disc drives and the like. In recent years, such a transport mechanism has also been adopted in apparatuses for driving optical discs, such as CD-ROM drives and the like. That is, in such an optical disc drive, in order to linearly reciprocate an optical pickup which performs reading and writing with respect to the optical disc, an engaging projection provided on the optical pickup is slidably engaged with a helical slot in a screw shaft, and the screw shaft is rotated in normal and reverse directions by a stepping motor, whereby the optical pickup can be transported along the axial direction of the screw shaft through the engaging projection.
FIG. 10 schematically illustrates a conventional optical pickup transport mechanism of this type. Referring to FIG. 10, one side of the optical pickup 1 is slidably supported by a guide shaft 2, and on the other side of the optical pickup 1, there are provided an engaging projection 4 for slidably engaging the optical pickup 1 with a helical slot 3a in a screw shaft 3, and a follower spring 5 for elastically bringing the optical pickup 1 into contact with the screw shaft 3 from the opposite side of the engaging projection 4. Since the engaging projection 4 is pressed into the helical slot 3a using a reaction force of the screw shaft 3 received from the follower spring 5, when the screw shaft is rotated in the normal and reverse directions by a stepping motor (not shown), the engaging projection 4 reciprocates in directions perpendicular to the surface of FIG. 10 while being guided by the helical slot 3a. Therefore, the optical pickup 1 can be transported in consistent directions through the engaging projection 4.
According to the above conventional optical pickup transport mechanism, the optical pickup 1 jumps up counterclockwise, as shown in FIG. 10 against a resilient force of the follower spring 5 when an external shock is applied thereto, so that the engaging projection 4 tends to disengage from the helical slot 3a in the screw shaft 3. Therefore, when impact force is applied to the optical pickup 1 in the direction perpendicular to the surface of FIG. 10, the optical pickup 1 supported by the guide shaft 2 alone may slide to a limit point in the transport range to collide with other members. When the optical pickup 1, which is a precision device including lenses, etc., collides with other members, trouble such as deviation of optical axis or damage to the optical pickup 1 tends to occur, so that product reliability may decrease.